Abstract: Different annealing processes were used to heat treat the hot rolled TC4 sheet. The effects of annealing temperature and the holding time on the microstructure and properties of the sheet were analyzed and compared. The results show that the grain equiaxed degree of the TC4 sheet increases with the increase of annealing temperature, while the tensile strength and elongation change little, the yield strength decreases obviously and the hardness increases considerably. The microstructure changes from equiaxed to bimorphic type when the annealing temperature is higher than 900 ℃. When annealed at 900 ℃ for 4 h, the grain size increases rapidly, the plasticity can be improved by prolonging the holding time, while the strengths are affected a little. When the holding time is prolonged at 950 ℃, the hardness of the sheet increases greatly; when annealed below 900 ℃ and the holding time is prolonged, the hardness increases slightly.

Key words: TC4 titanium alloy, annealing treatment, microstructure, mechanical properties